1. Field of the Invention
The present invention relates to a temperature detection circuit and, more particularly, to a temperature detection circuit for detecting whether or not a detected temperature has exceeded a predetermined specific temperature by using the temperature coefficient of the forward voltage drop of a diode. The present invention also relates to a semiconductor device having such a temperature detection circuit.
2. Description of the Related Art
A semiconductor device provided with a temperature detection circuit is known in the art. FIG. 7 shows the configuration of a conventional temperature detection circuit used in a semiconductor device. The temperature detection circuit, generally designated at numeral 200, includes a comparator 201, resistors R21 to R23 and a diode D21. The resistors R21 and R22 are connected in series between a high-potential power source line, to which a constant voltage is supplied from a constant voltage source, and a low-potential power source line configuring a ground line. The resistor R23 and the diode D21 are connected in series between the high-potential power source line and the low-potential power source line, with the diode D21 being forward biased. One of the input terminals, non-inverting terminal, of the comparator 201 is connected to a node N21 connecting the resistors R21 and R22 in series, and the other of the input terminals, inverting terminal, thereof is connected to a node N22 connecting together the resistor R23 and the anode of the diode D21.
The forward voltage drop of the diode D21 has a negative temperature coefficient, and the potential of the node N22 connected to the inverting input terminal of the comparator 201 is lowered with a rise of the ambient temperature. On the other hand, the voltage of the node N21 connected to the non-inverting input terminal of the comparator 201 is generated by a resistive voltage divider dividing the potential difference between the high-potential voltage and the low-potential voltage by the resistors R21 and R22, and is a constant voltage independent of the ambient temperature. For example, if the temperature to be detected is 90 degrees C., resistance ratio between the resistors R21 and R22 is adjusted so that the potential of the node N21 is as high as the potential of the node N22 at a temperature of 90 degrees C. In this case, by detecting whether the potential of the node N22, which varies depending on the ambient temperature, is higher or lower than the potential of the node N21, which is independent of the ambient temperature, it is detected whether the ambient temperature is higher or lower than 90 degrees C.
A conventional technique for detecting two and more temperatures by using a temperature detection circuit is described in Patent Publication JP-A-2003-108241A. FIG. 8 shows the configuration of the temperature detection circuit described in the patent publication. The temperature detection circuit, generally designated at numeral 300, includes a first comparator CA and a second comparator CB. A resistor R33 and a diode D31 are connected in series between a power source line having reference voltage VR0 output from a bandgap circuit 310 and the ground line. The node connecting together the resistor R33 and the anode of the diode D31 is connected to the inverting input terminal of the first comparator CA via a resistor R34. Further, the node connecting together the resistor R33 and the anode of the diode D31 is connected to the inverting input terminal of the second comparator CB via a resistor R37.
A reference voltage VR1 generated by a resistive voltage divider dividing the reference voltage VR0 by the resistors R31 and R32 is input to the non-inverting input terminal of the first comparator CA. Further, a reference voltage VR2 generated by a resistive voltage divider dividing the reference voltage VR0 by resistors R35 and R36 is input to the non-inverting input terminal of the second comparator CB. These reference voltages VR1 and VR2 have respective constant voltages independent of the ambient temperature. On the contrary, potential V31 of the node connecting together the diode D31 and the resistor R33, input to the inverting input terminal of the first comparator CA, varies depending on the ambient temperature, and potential V32 of the node connecting together the diode D31 and the resistor R33, input to the inverting input terminal of the second comparator CB, varies depending on the ambient temperature.
The reference voltage VR1 generated by the resistors R31 and R32 corresponds to the potential V31 of the node connecting the diode D31 and the resistor R33 at a first specific operating temperature, and if the operating temperature of the semiconductor device exceeds the first specific temperature, the output of the first comparator CA is inverted. Further, the reference voltage VR2 generated by the resistors R35 and R36 corresponds to the potential V32 of the node connecting the diode D31 and the resistor R33 at a second specific operating temperature, and if the operating temperature exceeds the second specific temperature, the output of the second comparator CB is inverted.
In the above-described patent publication, it is described that the second specific temperature is set at 130 degrees C. which is the guaranteed temperature for a suitable operation of the semiconductor-integrated circuit, and that the first specific temperature is set at 100 degrees C. which is slightly lower than the second specific temperature. Further, it is also described that when a microcomputer that controls the semiconductor-integrated circuit detects that the operating temperature exceeds the first specific temperature based on the output of the first comparator CA, the control unit judges that the operating temperature of the semiconductor-integrated circuit comes close to the upper limit of the guaranteed temperature range for a suitable operation, and thus, carries out a variety of processings such as transition of the operational mode of the semiconductor-integrated circuit into a power save mode.
In the temperature detection circuit 200 shown in FIG. 7, it is difficult to accurately predict, by calculations, the potential of the node N22 at which the output of the comparator 201 is inverted at a desired specific temperature, because the forward voltage drop of the product diode D21 varies due to the process conditions of the semiconductor-integrated circuit. Further, there is also a significant range of variation in the offset voltage of the comparator 201. Thus, if the resistance ratio between the resistors R21 and R22 defining the potential of the node N21 is set based on the potential of the node N22 obtained by calculations, there is a problem in that the accuracy of temperature detection is lowered due to a significant error caused by the range of variation.
In order to avoid the problem as described above and to thereby improve the accuracy of temperature detection, the resistance ratio between the resistors R21 and R22 of the resistive voltage divider is usually adjusted with the ambient temperature being maintained at the desired specific temperature. More specifically, for example, the resistor R21 is configured by a programmable resistor, the temperature detection circuit 200 is operated with the ambient temperature being maintained at the desired specific temperature, and the resistance of the resistor R21 is adjusted by using a fuse-cut technique so that the output of the comparator 201 is inverted exactly at the desired specific ambient temperature. In this manner, influences of the range of variation in the forward voltage drop of the diode D21 and the offset voltage of the comparator 201 can be avoided, to thereby improve the accuracy of the temperature detection.
If only one specific temperature is to be detected by the temperature detection circuit, the process of adjustment of resistance ratio is needed only once. However, if there are a plurality of desired specific temperatures, as in the case of the temperature detection circuit 300 shown in FIG. 8, resistance ratio must be adjusted at each of the desired specific temperatures. More concretely, in the temperature detection circuit 300, resistance ratio between the resistors R31 and R32 for detecting the first specific temperature is needed to be adjusted with the ambient temperature being maintained at the first specific temperature, and the resistance ratio between the resistors R35 and R36 for detecting the second specific temperature is needed to be adjusted with the ambient temperature being maintained at the second specific temperature.
Usually, in typical semiconductor devices, an environmental test is carried out as the wafer test at the upper limit of the guaranteed temperature range for a suitable operation, to thereby determine pass or fail of the products. If it is desired to detect the upper limit of the guaranteed temperature range for a suitable operation by using the temperature detection circuit, the upper limit can be detected by varying the resistance ratio between the resistors for detecting the upper limit of the guaranteed temperature range in the wafer test. However, if it is desired to detect the specific temperature, which is 100 degrees C. in the case of the above-described patent publication and slightly lower the upper limit temperature 130 degrees C., in addition to the upper limit temperature, the adjustment of the resistance ratio at 100 degrees C. is needed in addition to the adjustment thereof at 130 degrees C. In this case, there is a problem in that the productivity rate of the semiconductor devices is lowered because the adjustment of the resistance ratio at the temperature of 100 degrees C., which is not originally intended for the wafer test, is additionally needed.
In recent years, development of the semiconductor devices has been directed to multiple and diversified functions of the semiconductor devices, and the number of specific temperatures desired to be detected by the temperature detection circuit is increasing. Thus, in the temperature detection circuit, the resistance ratio between the resistors should be adjusted in a plurality of steps corresponding to the increased number of the specific temperatures to be detected. Accordingly, there arises a problem in that the productivity rate of semiconductor devices is lowered by using the conventional temperature detection circuit, because the number of adjustments for the resistance ratio therein is increased along with the increasing number of the desired specific temperatures.